Polymorphisms in the MLL breakpoint cluster region (BCR).

Area of Science:

• Genetics
• Oncology
• Molecular Biology

Background:

• The MLL gene is implicated in chromosomal translocations causing acute myeloid and lymphoid leukemia.
• Treatment-related acute myeloid leukemia (t-AML) can arise in patients receiving DNA topoisomerase II (topo II) inhibitors for primary malignancies, often involving MLL gene rearrangement.
• It remains unclear if patients have a heightened susceptibility to anti-topo II drugs or if t-AML is a random adverse event.

Purpose of the Study:

• To identify genetic polymorphisms that might predispose individuals to developing t-AML.
• To investigate the role of MLL gene variations in the context of topo II inhibitor treatment.

Main Methods:

• Sequencing of the MLL breakpoint cluster region (BCR) in patients who developed t-AML after topo II inhibitor treatment, control patients, and healthy individuals.
• Identification and analysis of polymorphic sites within Alu repetitive elements in the MLL BCR.

Main Results:

• Four polymorphic sites were identified within Alu elements: three affecting poly-A tract length and one altering a trinucleotide repeat (GAA).
• Poly-A tract polymorphisms showed no difference in frequency between leukemic patients and controls.
• The GAA trinucleotide repeat polymorphism, specifically the (GAA)4/5 heterozygote status, was more frequent in adult t-AML patients (83%) compared to the normal population (55%), although this association was not statistically significant due to small sample sizes.

Conclusions:

• Poly-A tract polymorphisms within the MLL BCR do not appear to be predictors of t-AML risk.
• A trinucleotide GAA repeat polymorphism in the MLL BCR shows a suggestive, but not statistically significant, association with t-AML development in patients treated with topo II inhibitors.
• Further research with larger sample sizes is needed to confirm the association between MLL gene polymorphisms and t-AML susceptibility.